The invention concerns a system for connecting a first fixed telephone network to a second fixed telephone network via a mobile telephone network incorporating one or more satellites, a plurality of xe2x80x9cfixedxe2x80x9d mobile telephone terminals replacing a cable connection conventionally called a trunk when it connects two exchanges. Each xe2x80x9cfixedxe2x80x9d mobile telephone terminal implements functions analogous to those of a conventional portable mobile telephone terminal but can be connected via a local exchange of the second fixed telephone network to any fixed terminal of the second fixed telephone network, rather than being used by a single user.
The system of the invention can be used to connect a national public telephone network to a regional public network serving a town in an isolated region where installing a cable or some other terrestrial infrastructure would be too costly. The original network includes at least one exchange serving a group of fixed user terminals and routing calls arriving from the first network. Because the user terminals are not used continuously, each xe2x80x9cfixedxe2x80x9d mobile telephone terminal is used in succession for different user terminals. A plurality of mobile telephone terminals can share the same frequency band on a time-division or code-division basis.
The invention is more particularly concerned with mobile radio networks of a type derived from the GSM type and including a geostationary satellite or non-geostationary satellites. Networks of the GSM type and derived types have the following features:
Each geographical area is divided into cells to enable carrier frequencies to be re-used.
A gateway manages the resources of each cell in terms of carrier frequencies and the channels carried by each carrier frequency.
At least one mobile radio service switching center manages calls, connections to the fixed telephone network and databases containing the mobile station ISDN directory number (MS-ISDN), the International Mobile Subscriber Identity (IMSI) and the location of each mobile subscriber, using databases known as the Visitor Location Register (VLR) and the Home Location Register (HLR).
Conventional GSM networks and networks derived from them are not designed so that more than one subscriber can use the same user terminal. Users personalize their terminal by inserting into it a Subscriber Identification Module (SIM) card containing an IMSI which determines the account to which calls are billed. After an initialization phase, the terminal is designated in radio messages by a Temporary Mobile Subscriber Identity (TMSI) which preserves the anonymity of the user. An authentication procedure uses a secret key stored in the SIM card to prevent fraudulent misuse of the IMSI or the TMSI of another user when a call is sent and when a call is received.
Using a plurality of xe2x80x9cfixedxe2x80x9d mobile telephone terminals to link first and second fixed telephone networks gives rise to the problem of coordinating the mobile telephone terminals, because it must not be possible for more than one mobile telephone terminal to attempt to receive the same call.
The problem also arises of selecting a user terminal at the time of an incoming call because, in a conventional GSM network, a radio link transmits a number designating the called radio terminal when a call to a radio terminal is set up. In no case is there any provision for transmitting a number for discriminating between a plurality of user terminals connected to the same xe2x80x9cfixedxe2x80x9d mobile telephone terminal via a local exchange of the second network.
The aim of the invention is to propose a system that addresses the above problems.
The invention consists firstly in a transfer control point for use in a system for connecting a telephone switch in an isolated region to a fixed telephone network via trunks supported by a plurality of xe2x80x9cfixedxe2x80x9d mobile telephone terminals of a mobile telephone network, a plurality of user terminals being connected to the telephone switch, at least one transfer control point connecting the fixed telephone network and a mobile services switching center which is part of the mobile telephone network, the mobile services switching center connecting all the trunks supported by the xe2x80x9cfixedxe2x80x9d mobile telephone terminals to the transfer control point, the transfer control point including:
means for making calls to the xe2x80x9cfixedxe2x80x9d mobile telephone terminals, and
means for dynamically managing the assignment of the trunks supported by the xe2x80x9cfixedxe2x80x9d mobile telephone terminals to telephone calls set up between the fixed telephone network and the user terminals connected to the switch in an isolated region,
and being characterized in that it further includes means for transmitting the international mobile subscriber number of a mobile telephone terminal to the mobile services switching center by placing that number in the xe2x80x9ccalled addressxe2x80x9d field of the SETUP message sent when setting up a connection supported by one of the xe2x80x9cfixedxe2x80x9d mobile telephone terminals.
The above transfer control point coordinates the mobile telephone terminals by placing a number designating a fixed radio terminal in the xe2x80x9ccalled addressxe2x80x9d field of the SETUP message sent to a switching center when a connection is set up.
In a preferred embodiment of the invention, a transfer control point is characterized in that it further includes means for transmitting the directory number of the called user terminal to the mobile services switching center by placing that number in the xe2x80x9ccalled sub-addressxe2x80x9d field of the SETUP message sent when setting up a connection supported by a xe2x80x9cfixedxe2x80x9d mobile telephone terminal.
In a preferred embodiment of the invention, a transfer control point is characterized in that it further includes means for forwarding to a local exchange of the fixed telephone network the directory number of a user terminal of the fixed telephone network when that terminal is called by a user terminal which is connected to the switch in the isolated region by placing that number in the xe2x80x9ccalled addressxe2x80x9d field of a SETUP message sent to said local exchange when setting up a connection supported by a xe2x80x9cfixedxe2x80x9d mobile telephone terminal.
The invention consists secondly in a xe2x80x9cfixedxe2x80x9d mobile telephone terminal for use in a system for connecting a telephone switch in an isolated region to a fixed telephone network via a plurality of xe2x80x9cfixedxe2x80x9d mobile telephone terminals of a mobile telephone network, a plurality of user terminals being connected to the telephone switch, at least one transfer control point connecting the fixed telephone network and a mobile services switching center which is part of the mobile telephone network, the mobile services switching center connecting all the trunks supported by the xe2x80x9cfixedxe2x80x9d mobile telephone terminals to the transfer control point,
characterized in that it includes means for extracting from a SETUP message the directory number of a called user terminal which is connected to the switch in the isolated region, and for sending that number to the switch in an isolated region in the form of a conventional signaling message.
The above xe2x80x9cfixedxe2x80x9d mobile telephone terminal allows direct inward dialing in the case of a call from a terminal of the fixed telephone network to a terminal connected to an exchange in the isolated region.
The invention consists thirdly in a mobile services switching center for use in a mobile telephone network including xe2x80x9cfixedxe2x80x9d mobile telephone terminals connected to a telephone switch to which a plurality of user terminals in an isolated region is connected, at least one transfer control point connecting that mobile telephone network to a fixed telephone network, all the trunks supported by the xe2x80x9cfixedxe2x80x9d mobile telephone terminals terminating at the transfer control point,
characterized in that it includes:
means for extracting the mobile subscriber directory number of a xe2x80x9cfixedxe2x80x9d mobile telephone terminal from the xe2x80x9ccalled addressxe2x80x9d field of a SETUP message from the transfer control point,
means for extracting the mobile directory number of a called user terminal from the xe2x80x9ccalled sub-addressxe2x80x9d field of the SETUP message from the transfer control point,
means for paging the mobile telephone terminal corresponding to that number,
means for preparing a new SETUP message by placing the mobile subscriber directory number of the xe2x80x9cfixedxe2x80x9d mobile telephone terminal in the xe2x80x9ccalled addressxe2x80x9d field of that message and by placing the directory number of the called user terminal in the xe2x80x9ccalled sub-addressxe2x80x9d field of that message, and
means for sending that message to the xe2x80x9cfixedxe2x80x9d mobile telephone terminal.
The mobile services switching center enables direct inward dialing to any terminal connected to the exchange in an isolated region by an incoming call from a user terminal which is part of the conventional telephone network.
The invention consists fourthly in a mobile services switching center for use in a mobile telephone network including xe2x80x9cfixedxe2x80x9d mobile telephone terminals connected to a telephone switch to which a plurality of user terminals in an isolated region is connected, at least one transfer control point connecting that mobile telephone network to a fixed telephone network, the mobile services switching center connecting the trunks supported by the xe2x80x9cfixedxe2x80x9d mobile telephone terminals to that transfer control point,
characterized in that it includes:
means for extracting the directory number of the transfer control point from the xe2x80x9ccalled addressxe2x80x9d field of a SETUP message from the switch,
means for extracting the directory number of a called user terminal which is part of the fixed telephone network from the xe2x80x9ccalled sub-addressxe2x80x9d field of the SETUP message from the switch, and
means for preparing another SETUP message and forwarding the extracted directory number to the transfer control point by placing it in the xe2x80x9ccalled addressxe2x80x9d field of that other SETUP message.
The above mobile services switching center enables direct inward dialing to a user terminal which is part of the conventional telephone network by an incoming call from a terminal connected to the exchange in the isolated region.